Acidity is an environmental condition commonly encountered by lactic acid bacteria and bifidobacteria in the gastrointestinal tract and fermented foods. In the present study, 22 strains of Bifidobacterium were screened for acid tolerance in artificial gastric juice (AGJ, pH 3·0) and fermented milk. AGJ tolerance was found to be strain-specific, with a pronounced variation among the strains. Several strains with a high survival rate in AGJ that belonged to Bifid. longum, Bifid. breve and Bifid. adolescentis were selected. Among them, only strain BL1 of Bifid longum was found to possess a high survival rate in fermented milk during refrigerated storage. Strain BL1 exhibited a survival rate of more than 25% in AGJ at pH 3·0 for 2 h and maintained a viable cfu level of more than 108 per gram of product in fermented milk (pH 4·6) under refrigerated conditions for 2 weeks. The acid tolerance of strain BL1 was found to depend on the final growth pH (<4·5). Rapid loss of acid tolerance was observed when the cells were shifted from acid to neutral conditions by addition of NaOH. Strain BL1 cells were able to maintain much higher intracellular pH under acid conditions, in comparison with those of AGJ sensitive mutant (BL1-S) or cells that lost acid tolerance following pH shifting from acid to neutral conditions. These results suggested that a cytoplasmic pH homeostasis system may function in the acid tolerance response in this strain.

Two kinds of measuring method of the high-power characteristics of piezoelectric transducers are described. One is the measurement method at the resonance frequency and another is the measurement method at the antiresonance frequency. The vibrational velocity dependences of the equivalent circuit constants and the temperature rise were measured by using each measurement method under the constant vibrational velocity control. These results are useful for designing the ultrasonic power devices such as the ultrasonic motor, and also useful for investigating the new advanced piezoelectric materials for high power use. Especially, by using the results obtained at the antiresonance frequency, a stable state driving method, named as antiresonance driving, with high-efficiency and low-temperature rise can be achieved.

Electro-mechanical properties in the pseudo-ternary solid solution system of PbZrO3-PbTiO3- Pb(Mn1/3Sb2/3)O3 piezoelectric ceramics were studied by changing the vibration- level using a constant current / velocity driving method. The vibration velocity is proportional to the driving electric field under a relatively low field. The velocity, however, deviates from a linear relationship as electric field increases and converges on a certain value.

The increase of the vibration-level is accompanied by a large amount of heat generation as well, and this heat generation sets a practical upper limit of the vibration-level. The heat generation is caused by a dissipated-vibration-energy which is represented as a function of vibration velocity and the constants depending on the materials and transducers.

In these pseudo-ternary solid solution ceramics, the compositional ratio which shows excellent electro-mechanical properties under a relatively low vibration-level does not necessarily coincide with the compositional ratio which is excellent under a relatively high vibration-level.